These issues haven't changed since the 2018 Photoshop cc upgrade (Mac version. For PC version, I wouldn't know). When using a 3D Color Lookup at the top of the layer stack (.cube file) and subsequently trying to use Color Range underneath, virtually every color is chosen except for the pixel that's clicked on. This is hugely annoying, especially when working with a large layer stack. Only when the 3D Color Lookup layer is switched off will the Color Range function work properly again. Also, bug number two, when needing to use two 3D Color Lookup layers in the same layer stack (when matching to reference in a different color space for example), Photoshop slows down to an impossible crawl once the file is barely even a GB in size. These issues really need to be sorted out. Thanks.

Would you be able to share any sample files to test with?Or perhaps a video describing your workflows?

Since you've written two bug reports here regarding 3d LUTs, it'd be best if you split the report into two separate threads so we can track the potential bugs individually. This will help move towards a fix in a quicker fashion.

Hi again... Yes, just to be clear it's the very latest Photoshop (double checked this morning) and the very latest Mac OS. I'm not even sure what there is to add regarding workflow. I thought it might be due to working with a large file & layer stack. However, the video I uploaded for you (see my post below) was made with a single layer & a few adjustment layers on top. The Color Lookup could have been any .cube file.

This is independent of Mac OS (I recently upgraded to High Sierra, though this was also happening with the Regular Sierra before that). I was having a discussion with another matte painter, also in the film visual effects industry with exactly the same issue, though he's using Windows. It seemed to stem (in our case from .cube files generated in Nuke & used as Color Lookups in Photoshop). However, more worryingly, I've now had exactly the same problem, but because of one single offending curves layer. Anyway, I'm posting a simple screen grabbed clip of the problem. Hopefully it will have processed to a decent resolution by the time you see it.

Sorry, I came to this a bit late. Good questions. The answer to the first one is yes, I have tried, and it makes no difference.The answer to the second one is, no I hadn't tried. I have since done so by changing to greyscale, and it seems that it does indeed pick the correct selection based on the pixel chosen. However, in greyscale it works with just the one click, but as the display is now in greyscale, it kind of limits the color pick options if you initially chose the wrong one. It's nearly as cumbersome as swithcing off the offending color lookup layer or layer adjustment to compensate. Good to know, but it's only a marginal work around.The color range should really be working at the get-go to be honest.

I take back what I last said. Color range with greyscale (with color lookup layer switched on) doesn't actually function either. Was using it "in anger". Didn't work.Had to "unlike" your comment. Sorry. ADOBE...Please sort this out.The work around I have is to place the corner of a menu next to an offending pixel in order to be able to see it and choose it without a color lookup. Crap really.